It's nothing new that humanity is getting chubbier by the day. What's surprising is that we're bringing our animals along for the ride. A meta-analysis of animal weight has revealed that, over the last several decades, creatures as diverse as feral rats and laboratory primates have been getting fatter.
For some of the species in the study, these trends have obvious causes. Dogs and cats are moving less and watching more tv, just like their owners. 'Synanthropes', animals like pigeons and rats that live in association with human communities, are thriving on dumpsters filled with our calorie-dense discards. Without natural predators keep them on their toes, it makes sense that city rats living on fatty, sugary foods will turn into the rodent equivalents of Howard Taft.
It's harder to explain weight gain in lab animals. Creatures used in research settings like chimpanzees, macaques and vervets all live in controlled environments where they're insulted from the charms of Krispy Kreme and HBO. These zaftig animals typify the complex state of obesity science. One day obesity is reducible to maxims – "eat less, exercise more" – while the next it balloons outwards to encompass hidden factors like viruses, thrifty genes, drifty genes, and chemical obesogens.